This application claims priority to prior application JP 2002-88122, the disclosure of which is incorporated herein by reference.
This invention relates to an ion beam charge neutralizer and an ion beam charge neutralizing method in an ion implanter having a mechanism for linearly and reciprocally scanning an ion beam by an electric field or a magnetic field. This invention also relates to an ion beam charge neutralizer and an ion beam charge neutralizing method in an ion implanter having a mechanism for forming a sheet-like or a ribbon-like ion beam through an ion extracting member or a beam line.
In production processes of semiconductor integrated circuits, ion implanters are widely used because impurities can be accurately and precisely introduced into a microscopic area on a surface of a wafer. Since the ion implanter implants charged ions, i.e., ions having electric charges, into the wafer to be processed, there arises a problem of charge accumulation (charge-up) onto the wafer.
Generally, the ions to be implanted have positive electric charges. Therefore, in order to suppress the charge-up, negative electric charges (electrons) are supplied. For example, use is made of a method of actively supplying electrons produced by collision of ions against a wall of a beam line and another method of supplying secondary electrons produced near the wafer by the use of an electron gun. Among others, a plasma shower (or a plasma flood gun) is widely used as a method capable of supplying electrons having relatively low energy.
In a batch-type ion implanter, the wafer is placed on a rotary disk adapted to perform linear reciprocal movement so as to enable ion implantation throughout an entire surface of the wafer. In this event, a beam trajectory or orbit is fixed with respect to the beam line. The plasma shower is disposed in the vicinity of the beam. By the potential of the beam, the electrons are supplied from the plasma shower.
Referring to FIG. 1, description will be made of an existing plasma shower used in the batch-type ion implanter.
A plasma generating gas 16 is introduced into an arc chamber 15. A filament 17 is heated by a power supply 18 and an arc voltage 19 is applied between the filament 17 and the arc chamber 15. As a consequence, a plasma is generated in the arc chamber 15. Setting is appropriately made so that an ion beam 28 is located in the vicinity of the arc chamber 15. Then, electrons are extracted by a potential built up by the ion beam 28 so that the charge-up by the beam is suppressed. By arranging a shower tube 37 and applying a negative potential 38 to the shower tube 37, it is possible to promote the supply of electrons from the arc chamber 15 to the beam.
On the other hand, in an ion implanter having a mechanism for scanning the beam by making the beam itself perform linear reciprocal movement, the relative position of the beam and the plasma shower is continuously varied. This makes it difficult to stably supply the electrons. In view of the above, various methods are proposed in order to stably supply the electrons from the plasma shower to the scanned beam.
For example, in order to promote the supply of electrons to the ion beam scanned in a wide area from an ion beam charge neutralizer, proposal is made of various methods of applying a magnetic field to a beam scanning area.
In a first conventional technique (JP 7-176290 A), an extracting hole of a plasma arc chamber is arranged in parallel to a beam scanning direction. The magnetic field is applied by coils in parallel to the beam scanning direction.
In a second conventional technique (JP 8-190887 A), the plasma arc chamber is arranged at the center of the beam scanning area to be perpendicular to the beam scanning direction. A magnetic field spreading outward from the center is applied by coils.
In a third conventional technique (JP 9-147785 A), the plasma arc chamber is arranged at the center of the beam scanning area to be perpendicular to the beam scanning direction. A magnetic field spreading outward from the center throughout a whole of the beam scanning area is applied by coils.
In a fourth conventional technique (JP 10-27569 A), the plasma arc chamber is arranged at the center of the beam scanning area to be perpendicular to the beam scanning direction. An a.c. magnetic field synchronized with the beam reciprocation is applied by coils in parallel to the beam scanning direction.
In a fifth conventional technique (JP 10-172502 A), the third conventional technique is improved by providing an electric field for electron reflection. Furthermore, a magnetic field is applied in parallel to the beam scanning direction.
In each of the above-mentioned plasma showers, the supply of the electrons may be unintentionally prevented because the applied magnetic field itself excessively constrains or binds the electrons in some cases. In order to avoid such prevention of the supply of the electrons, the magnetic field must accurately and precisely be generated. However, it is not always easy to generate a magnetic field exactly as desired.
In order to synchronize beam reciprocation and the magnetic field, a complicated mechanism is required to form a circuit. In addition, it is difficult to confirm whether or not the trajectory of the electrons is controlled in the manner exactly as desired. Furthermore, in case where the coil is used, the mechanism itself is increased in scale.
As a sixth conventional technique (S. Sakai et al., International Conference on Ion Implantation Technology Proceedings, September 2000, pp. 592595), a radio frequency antenna is used to generate a plasma covering a wide area. In this event, a large-scale and complicated mechanism is required to produce, propagate, and control a radio frequency wave.
As a method of supplying the electrons extracted from the plasma arc chamber to the beam after the electrons are introduced into a secondary chamber, proposal is made of the following techniques.
In a seventh conventional technique (JP 2756704 B), a mesh-type electrode is arranged in the secondary chamber for the purpose of exclusively supplying low-energy electrons to the ion beam.
In an eighth conventional technique (JP 6-203788 A), low-energy secondary electrons produced as a result of collision of the extracted electrons against a wall of the secondary chamber are supplied to the ion beam by applying a magnetic field.
However, the seventh and the eighth conventional techniques are addressed to the batch-type ion implanter and do not intend the supply of electrons over a wide area.
It is therefore an object of this invention to provide a charge neutralizer, a charge neutralizing method, and an ion implanter comprising the charge neutralizer, which neutralizer is capable of stably supplying electrons to a scanned ion beam over a wide area by confining the electrons by the use of cusp magnetic fields generated by arranging a plurality of sets of permanent magnets.
It is another object of this invention to provide a charge neutralizer, a charge neutralizing method, and an ion implanter comprising the charge neutralizer, which neutralizer is capable of stably supplying electrons to a whole of a sheet-like or a ribbon-like ion beam over a wide area by confining the electrons by the use of cusp magnetic fields generated by arranging a plurality of sets of permanent magnets.
According to this invention, there is provided an ion beam charge neutralizer, in which electrons extracted from an arc chamber and pooled in an electron accumulating member are uniformly supplied throughout an entire area of a scanning area of the parallelized ion beam, which is extracted from an ion source as a normal ion beam, and the extracted normal ion beam is reciprocally scanned over a specific range in accordance with continuous-variable control drive of an electric field or a magnetic field, and the scanned ion beam is parallelized with an electric field or a magnetic field, and the parallelized ion beam is traveling towards a target object and comes down to the target object, the parallelized ion beam is neutralizing by the electrons that are supplied from the ion beam charge neutralizer.
According to this invention, there is also provided an ion beam charge neutralizing method, in which electrons extracted from an arc chamber and pooled in an electron accumulating member are uniformly supplied throughout an entire area of a scanning area of the parallelized ion beam, which is extracted from an ion source as a normal ion beam, and the extracted normal ion beam is reciprocally scanned over a specific range in accordance with continuous-variable control drive of an electric field or a magnetic field, and the scanned ion beam is parallelized with an electric field or a magnetic field, and the parallelized ion beam is traveling towards a target object and comes down to the target object, the parallelized ion beam is neutralizing by the electrons that are supplied from the ion beam charge neutralizer.
According to this invention, there is also provided an ion implanter comprising an ion beam charge neutralizer, in which-electrons extracted from an arc chamber and pooled in an electron accumulating member are uniformly supplied throughout an entire area of a scanning range area of the parallelized ion beam, which is extracted from an ion source as a normal ion beam, and the extracted normal ion beam is reciprocally scanned over a specific range in accordance with continuous-variable control drive of an electric field or a magnetic field, and the scanned ion beam is parallelized with an electric field or a magnetic field, and the parallelized ion beam is traveling towards a target object and is implanted onto the target object, the parallelized ion beam is neutralizing by the electrons that is supplied from the ion beam charge neutralizer.
According to this invention, there is also provided an ion beam charge neutralizer, in which electrons extracted from an arc chamber and pooled in an electron accumulating member are uniformly supplied throughout an entire area of a spread range of a sheet-like or a ribbon-like ion beam, which is extracted from an ion extracting member wide in one direction or is formed by enlarging a beam width on a beam line by an electric field or a magnetic field.
According to this invention, there is also provided an ion beam charge neutralizing method, in which electrons extracted from an arc chamber and pooled in an electron accumulating member are uniformly supplied throughout an entire area of a spread range of a sheet-like or a ribbon-like ion beam, which is extracted from an ion extracting member wide in one direction or is formed by enlarging a beam width on a beam line by an electric field or a magnetic field.
According to this invention, there is also provided an ion implanter comprising an ion beam charge neutralizer, in which electrons extracted from an arc chamber and pooled in an electron accumulating member are uniformly supplied throughout an entire area of a spread range of a sheet-like or a ribbon-like ion beam, which is extracted from an ion extracting member wide in one direction or is formed by enlarging a beam width on a beam line by an electric field or a magnetic field.
In the above-mentioned ion beam charge neutralizer according to this invention, the electrons are supplied in a third direction intersecting a beam traveling direction and a beam scanning direction to thereby neutralize electric charges of the ion beam.
In the above-mentioned ion beam charge neutralizer according to this invention, the electrons are supplied in a third direction intersecting a beam traveling direction and a beam spread direction of the sheet-like or the ribbon-like beam to thereby neutralize electric charges of the ion beam.
In the above-mentioned ion beam charge neutralizer according to this invention, the electrons for charge neutralization are produced by introducing a discharge gas into a plasma generating chamber so that arc discharge is caused by heating a filament and by applying an arc voltage in the plasma generating chamber to generate a plasma and the electrons are extracted from an extraction port of the plasma generating chamber by applying an electric field.
In the above-mentioned ion beam charge neutralizer according to this invention, the electrons for charge neutralization are supplied to the ion beam through an intermediate chamber as an electron accumulating member after the electrons are extracted from the plasma generating chamber and pooled in the intermediate chamber.
In the above-mentioned ion beam charge neutralizer according to this invention, the electrons for charge neutralization are supplied to the ion beam through an intermediate chamber as an electron accumulating member after the electrons are extracted from the plasma generating chamber and pooled in the intermediate chamber, which acts as an electron confinement area under cusp magnetic fields formed by permanent magnets. The intermediate chamber accumulates a large amount of electrons and supplies the electrons to the ion beam.
In the above-mentioned ion beam charge neutralizer according to this invention, a large amount of the electrons for charge neutralization accumulated in the intermediate chamber are extracted through a slit electrode or a multihole electrode having a series of holes to be supplied to the beam.
In the above-mentioned ion beam charge neutralizer according to this invention, the slit electrode or the multihole electrode is arranged on one side or both sides of the beam to be substantially coincident with a beam scanning direction for the scanned beam or to be substantially coincident with a beam spread direction for the sheet-like or the ribbon-like beam.
In the above-mentioned ion beam charge neutralizer according to this invention, the intermediate chamber as an electron confinement area under the cusp magnetic field is adapted to be applied with an electric voltage for promotion of electron supply to the ion beam.
In the above-mentioned ion beam charge neutralizer according to this invention, the slit electrode or the multihole electrode is adapted to be applied with an electric voltage for extraction of the electrons.
In the above-mentioned ion beam charge neutralizer according to this invention, a beam guide tube is adapted to be applied with a voltage for reflection of the electrons.
In the above-mentioned ion beam charge neutralizer according to this invention, the confinement area by the cusp magnetic fields is formed by placing permanent magnets in each of walls inside the intermediate chamber.
The ion implanter according to this invention comprises a plasma shower mechanism for easily and stably supplying electrons to a whole of a scanned beam or a sheet-like or a ribbon-like beam by introducing cusp magnetic fields. Generally, the cusp magnetic field is used to confine charged particles in anion source or the like. In this invention, the cusp magnetic field is mainly used to confine electrons and to equalize the concentration of the electrons over a wide area.
By the use of this invention, in an ion implanter having a beam scanning mechanism, it is possible to achieve a charge-up suppressing function sufficient for a device production process. This invention is also applicable to an ion implanter having a mechanism for forming a sheet-like or a ribbon-like beam.